1. Field of the Invention
The present invention relates to the treatment of wastewater, particularly wastewater effluent from household laundered wash or laundromats, as distinct from commercial laundry effluent.
2. Background and Discussion of the Prior Art
Laundromats desire to discharge their effluent to subsurface aquifers, or to the surface, or reuse the treated water as feedwater. Present day state and local environmental restrictions place severe limitations on the organic matter and solids permitted to be discharged to the environment. Laundromats desire an effluent treatment system which meets these present day rigorous environmental standards and yet permits essentially continuous operation with minimal downtime, and in which maintenance is achieved in a practical manner with minimal cost by persons of limited technical skill.
Environmental agencies in various locales throughout the country have recently set and enforced rigorous maximum discharge criteria standards for commercial wastewater. Laundromats in certain locales face the following wastewater effluent maximum permissible criteria:
______________________________________ MBAS .sub. 1.0 ppm TSS .sub. 30.0 ppm TDS 1000 ppm Oil and grease 15 ppm pH 6.5-8.5 ______________________________________
"MBAS" refers to "methylene blue active substances", "TSS" refers to "total suspended solids", and "TDS" refers to "total dissolved solids", as determined by conventional testing methods well-known to those skilled in the art. "FOG" refers to "fats, oils and greases." "Oil and grease" is understood to mean essentially "FOG".
Laundromats face a particularly onerous burden in meeting the aforesaid criteria insofar as a typical laundromat effluent discharge is between 8,000 to 35,000 gallons/day and has the following broad range of characteristics:
______________________________________ MBAS 35-130 ppm TSS 70-130 ppm TDS 350-775 ppm Oil and grease 30-80 ppm pH 8.5-11.0 ______________________________________
Commercial laundries, in contradistinction to laundromats, select and closely control the specific detergent and concentrations of same. Laundromats however are faced with the users' diverse detergents used in diverse concentrations. It has been found, by way of example, that detergent concentrations in the effluent are greater on weekends than on weekdays, and detergent materials and concentrations vary from moment to moment. Laundromats for the above and further reasons discussed infra have effluent discharge problems not generally faced in commercial laundry controlled operations.
One early attempt directed to a car wash or laundry effluent treatment is disclosed in U.S. Pat. No. 4,104,164, granted Aug. 1, 1978, to Chelton. Chelton disclosed a generalized approach to wastewater treatment. Chelton provided for a first stage treatment by a weir or gravity filtration of the effluent followed in seriatim by centrifugation, activated carbon adsorptive filtration, bag filtration and particulate filtration. Insofar as laundromat effluent particulates have a density close to that of water, the Chelton gravity filtration and centrifugation would effectively be inoperable for such use. It is doubtful that the Chelton system would be practical for laundromats, and could with any practical consistency ever meet the present stringent discharge standards before requiring extensive downtime and maintenance. Furthermore, by way of example, due to the types and concentration of contaminants present in laundromat wastewater, the Chelton activated carbon would be exhausted in a short period of time, necessitating extensive labor and expense to change the carbon bed. Other commercial laundry prior art systems were also directed to gravity and screens with oil/water separators as disclosed in U.S. Pat. No. 5,207,922, granted May 4, 1993, to McFarlan, et al. and U.S. Pat. No. 5,167,829, granted Dec. 1, 1992, to Diamond, et al. The treated 1992, to Diamond, et al. The treated water from these commercial laundry operations was generally discharged for further treatment at publicly owned treatment works.
U.S. Pat. No. 5,246,560, granted Sep. 21, 1993, to Dobrez, et al. disclosed a commercial laundry water treatment to remove FOGs in which a cationic coagulant is fed inline with monitoring of the electric charge value of the water-coagulant mixture. The treated water was like the afore-described prior art required to be transported to and further treated by publicly owned treatment works. This approach is not suitable for laundromats which must remove all requisite contaminants to satisfy the present environmental standards. German Patent No. 3,344,275, discussed in Dobrez, et al., disclosed a related method which required measuring diverse parameters of raw laundry wastewater and adding flocculent in response to cloudiness and adding alkali and/or acid in response to the measured pH value, with the pH of the wastewater adjusted to 7.5-9. These prior art treatment methods were unsuitable for laundromat operations or otherwise directed away from the present invention.
Commercial laundries may use amphoteric dicarboxylate amine based emulsifying detergents. Such detergent use is disclosed in U.S. Pat. No. 5,167,829, granted Dec. 1, 1992, to Diamond, et al. and U.S. Pat. No. 5,523,000, granted Jun. 4, 1996, granted to Falbaum, et al. Falbaum, et al. disclosed an organic soil removal method which employs a cationic flocculent in necessary operative combination with an amphoteric dicarboxylate detergent in a pH change protocol. Household, as opposed to commercial, laundry detergents and builders avoid such amphoteric dicarboxylate detergents because as amine derivatives they are subject to chelating with heavy metal compounds to form solubilized toxic materials. This is particularly so where the laundromats desire to recycle all or part of the treated effluent. Falbaum, et al., by virtue of requiring amphoteric dicarboxylates and creating such heavy metal toxicity, is inoperative for laundromat operations. See U.S. Pat. No. 3,870,648, granted Mar. 11, 1975, to Grifo at col. 3, lines 3-27 and col. 4, lines 9-15, for a discussion of this heavy metal toxicity problem in household laundered wash. The present invention avoids the introduction and use of toxic heavy metal chelating or solubilizing compounds such as amphoteric carboxylates which as amine derivatives chelate and solubilize toxic heavy metals. As a consequence, the treated water of the present invention is substantially free of toxic heavy metals, and may therefore be recycled to the laundromat or discharged to the environment.
The commercial laundry prior art, namely Falbaum, et al. and Diamond, et al., disclosed FOG separation or flocculation at exceptionally low pH values of about 1.5 to 4.5 in order to remove substantial FOGs to where the wastewater had a FOG concentration of about 100 ppm or lower. In marked contrast, laundromats require wastewater discharge with oil and grease concentrations of less than 15 ppm, and additionally require the substantial removal of other environmentally proscribed contaminants, in a moderate pH environment because such highly acidic environments necessitate specialized equipment and maintenance and are not suitable or practical for neighborhood laundromats.
A recent prior art system directed to treating laundromat effluent is shown in FIG. 1 infra. FIG. 1 shows a treatment system wherein laundry effluent 10 first passes through in-frame window screens 11 to remove large particulates, as was typical of the prior art. The screened wastewater is pumped by pump 12 to a multi-media or particulate filter 13 which contained diverse particulates such as sand, anthracite coal, and garnet. The filtered water was then transferred to ion exchange resin vessels 14, with a regenerant solution holding tank 15. Effluent 16 from vessels 14 was then transferred to leaching pools (not shown). A city source cold water backwash 17 to filters 13 and 14 was used. While the FIG. 1 system provided some improved treatment of the wastewater effluent, the quality of the effluent was inconsistent and the filters 13 and 14 would readily become clogged or fouled. The FIG. 1 system was not suitable for practical, cost effective laundromat operations.
Referring to FIG. 2 there is shown a more recent prior art wastewater treatment system for laundromats. The system, in general terms, comprises a laundromat wastewater effluent line 20, bag filters 21 disposed within lint trap 22, and pump 23 operably disposed in lint trap 22 pumps the lint trap outflow to a second bag filter 24. The second bag filtered water is then pumped by pump 37 to a multi-media or particulate filter 25 to remove suspended solids. The outflow 41 from filter 25 is pumped by pump 42 to a FOG removal or absorptive filter 26 which also removes residual fine solids. The FOG removed outflow water 40 from filter 26 is treated in a strong base anion exchange resin in vessels 27 to remove MBAS. Cold water backwash 63 is provided. A regenerant solution 28 containing a biocide and/or oxidative chemical 61 is introduced at 65 to vessels 27 during an automatic intermittent cleaning process to control bacterial growth and to reduce fouling of the ion exchange resin, and the spent regenerant 55 is discharged at 64. The fully treated effluent 29 from vessels 27 is sent to leaching pools (not shown) to subsurface aquifers, surface or for reuse or subsequent purification. The laundromat wastewater effluent 20 is first treated by relatively fine mesh filter bags 21. Bags 21 are rated at 100 to 800 microns, and preferably 100 to 400 microns, with about 300 microns being most preferred. Bags 21 are mounted to each bottom orifice 32 of opposed drop tees or joints 30 with an opposedly disposed top orifice 31. Any effluent overflow, such as by an aberrant surge in flow, passes through top orifice 31 directly into trap 22. The bags 21 are operatively disposed within trap 22 so that the filtered water passes first to a turbulent flow upper level 33. The filtered water contains residual organic matter agglomerates which water then flows from the turbulent flow upper level 33 to the quiescent flow lower level 34 of trap 22, whereat the agglomerates further settle out. Overflow 45 from trap 22 is gravity fed to overflow holding tank 46 where a pump disposed in tank 46 is operatively interlocked with a float in trap 22 to pump return flow to effluent feed line or pipe 20 for a continuous even flow operation. Pump 23 pumps the first bag filtered water 36 to a second bag filter 24. Second bag filter 24 is approximately the same mesh size as first bag filter 21. In a preferred embodiment of the invention, the second bag filter 24 is somewhat coarser than the first bag filter 21. The immediately afore-described prior art systems was generally directed to and relied on multiple filtration stages wherein the wastewater first underwent gross filtration by weir, gravity and/or screen means for removal of relatively large particulates and agglomerates. This approach however caused rapid clogging and fouling of the filters, particularly the FOG absorptive filter 26, and was proven impractical and inoperable for laundromat operations. Furthermore, it was found that the linear alkyl sulfonates (LAS) typical of household detergents bonded to the strong base anion resin in an essentially irreversible manner causing ineffective wastewater treatment.
The laundromat art thus desired a method and apparatus for treating its diverse wastewater effluent in an essentially continuous operation, in a non-toxic, moderate pH environment, and with minimal maintenance and downtime, and yet importantly meet the present day stringent environmental discharge standards. The present invention provides that desired result.